The present invention relates to a device for generating electric power from a source of air or other gas or fluid under pressure.
Devices for generating low-voltage electric power (typically, at 24V) using the energy provided by a source of air under pressure are currently available on the market. Such devices basically comprise an electric generator, a radial micro-turbine coupled for rotation with the rotor of the electric generator and a nozzle through which the air under pressure provided by a source of air under pressure is directed against the blades of the micro-turbine so as to drive the micro-turbine into rotation, along with the rotor of the electric generator, thereby producing electric power from the pressure and kinetic energy of the flow of air under pressure. Such devices further comprise an electronic control unit arranged to ensure a constant output voltage independently of changes in the electric load connected to the device and in the pressure of the air under pressure supplied to the device. The arrangement of the micro-turbine in series with the electric generator makes the device rather bulky, in particular in the axial direction (i.e. in the direction of the axis of rotation of the micro-turbine and of the rotor of the electric generator).
An electric generator for an air tool is known from U.S.2005/0258694 and comprises a rotor provided with blades and an annular stator axially arranged between the rotor and a bearing for support of the rotor, wherein the rotor has, on its end face axially facing towards the stator, a plurality of cylindrical cavities which extend parallel to the axis of the rotor and accommodate each a respective permanent magnetic body (made for instance of neodymium-iron-boron) of cylindrical shape inserted into a respective non-magnetic body (made for instance of zinc, aluminium or brass) of cup-like shape. This known solution is however also affected by the drawback of the great axial size, since the stator is arranged axially at the side of the rotor. Moreover, this known electric generator has a high number of components.
A device for generating electric power from a source of air or other gas or fluid under pressure having the features set forth in the preamble of the enclosed independent claim 1 is known from U.S.2009/0224544. According to this known solution, the device comprises a plurality of permanent magnets mounted on the outer surface of a cylindrical support structure inside which the impeller of the turbine is inserted. The permanent magnets are anisotropic and have a fixed axis of magnetization, whereby they can only generate a radial magnetic field. Each pair of permanent magnets creates therefore two poles and accordingly the device will have a number of pole pairs proportional to the number of permanent magnets. Since the frequency of the electric current produced is proportional to the rotational speed and to the number of pole pairs and since a high frequency of the current may cause high hysteresis losses and high losses in the diodes of the rectifier bridge, such a known device is therefore not suitable for working at high speed.